1. Field of the Invention
Aspects of the present invention relate to a measuring device and a method for measuring the deposition thickness of α-Si on a substrate during a semiconductor fabrication process.
2. Description of the Related Art
Plasma enhanced chemical vapor deposition equipment (hereinafter, simply referred to as “PECVD” equipment) produces a substrate by depositing a buffer and amorphous silicon (hereinafter, simply referred to as “α-Si”) to a glass during a low temperature polysilicon fabrication process. The deposition thickness of α-Si is closely related to a silicon crystallization process of producing polysilicon. In more detail, the deposition thickness of α-Si affects the determination or setting of energy density of an excimer laser annealing (ELA) equipment that is used as a silicon crystallization equipment. However, since the energy density of the ELA equipment is not typically determined or set according to the deposition thickness of α-Si that is deposited during a present silicon crystallization process, if the deposition thickness of α-Si of the present silicon crystallization process is different from a target deposition thickness of α-Si that was previously established in the ELA equipment for a prior silicon crystallization process, a line spot defect occurs in a substrate after the present silicon crystallization process is completed. Therefore, in order to reduce the line spot defect that is one of the main defect items that occurs during silicon crystallization processes, it is necessary to reduce the distribution of or the variance in the deposition thickness of α-Si.
When a run-to-run (RtR) control method, which is one of the advanced process control (APC) technologies that are widely used for the semiconductor fabrication process, is used with the PECVD equipment, the distribution of or variance in the deposition thickness of α-Si can be reduced compared to a typical existing semiconductor fabrication process. The RtR control method effectively removes disturbances that occur during the semiconductor fabrication process, thereby improving the process ability of the PECVD equipment. However, if there is a loss of the measured data or a delay in the measurement of the deposition thickness of α-Si, the performance of the RtR control method can be reduced.
After the silicon crystallization process is completed, a thickness ellipsometer is used to measure the deposition thickness of α-Si. In general, since at least two chambers of the PECVD equipment share a single thickness ellipsometer, time is spent to carry a substrate between the chambers and the thickness ellipsometer besides time that is spent to measure the deposition thickness of α-Si. That is, it is impossible to know the deposition thickness of α-Si in each substrate immediately after the α-Si is deposited in the PECVD equipment. Also, when the number of substrates that are provided in the PECVD equipment increases, it is impossible to measure the deposition thickness of the α-Si for every substrate.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore contain information that is not necessarily prior art that is already known in this country to a person of ordinary skill in the art.